The Youth in Arts a cappella ensemble ‘Til Dawn appears in “Sing Out!” this weekend at the Marin Country Mart in Larkspur. A fundraiser for ‘Til Dawn’s scholarship program, Friday’s concert begins at 6 p.m., bringing together singers from the current group along with alumni from past seasons in a 90-minute program spanning original works and classics by Stevie Wonder, Joni Mitchell, Gnarls Barkley, Eurythmics, Bill Withers and others.